What phone did you have before though?? As far as i can see (my mate has one) it doesnt really seem worth upgrading to the iphone4 from a 3gs with the new os4 installed. Better screen - not that the 3gs is at all crappy, flash on camera, but who really uses an iphone for great pics? And battery life apparently improved...
My contract is up pretty much now on my 3gs but after seeing one in the flesh i am having second thoughts about upgrading. It is a tad narrower and thinner but it doesnt feel it in your hand because of the square non rounded edges compared to the 3g/3gs. It looks nice but certainly doesnt feel as good in your hand.
Been thinking i might just save about £30 per month and go on a simplicity with my current 3gs....